Hello Maria,
I ship pack to US from istanbul. I have same problem with USPS since December 2010. USPS used to record all activities of international posts on their tracking page until 12/2010 but then never records, just a notice "origin post is preparing shipment" on tracking page, in spite of the pack is about delivered.
USPS records the last activity after delivery, unfortunately.
Because of this reason, I inform and warn my US customers about this problem with a note of invoice.
Seller looks as offender to the customers with this problem until delivery, unfortunately.
Best,
PRP